Over the last few decades, roads, homes, commercial buildings have cut across the wide, open spaces of the West. And that development is having an impact to many of the species that live there, especially the pronghorn antelope, especially in one of the fastest-growing areas in the Southwest: Arizona's Prescott Valley. From the HERE AND NOW Contributors Network, Laura Morales at KJZZ's Fronteras Desk reports.

LAURA MORALES, BYLINE: Jim McClasland has lived in Prescott Valley for more than five decades. And he's watched it change from his front porch.

JIM MCCLASLAND: If you stand here and look, you can see (unintelligible) see this. There's no buildings. There's no people. There's no - there's not all these trees. It was just wide-open country.

MORALES: And thousands of pronghorn antelope were free to roam. Today, the valley is packed with houses and strip malls. When McClasland bought a house, he decided to live on the outskirts of town to enjoy the wildlife.

MCCLASLAND: But at the same time I took habitat, and I consciously knew that I was doing that. But I also consciously did not put up a fence. This fence that my neighbor has affects movement of wildlife. It just does.

MORALES: I take a drive with the Arizona Game and Fish Department's Virginia Gouldsbury and Zen Mocarski. They show me how those fences fragment pronghorn habitat. We drive beyond the fences to where we hope to see antelope. I have my camera ready. We have trouble finding them. It's fawning season so many females are bedded down, ready to have their babies. But there are also fewer antelope here today. Researchers once estimated 5,000 antelope in this area. Today, there are only about 1,000 in Prescott Valley.

We just drove past a subdivision called Pronghorn Ranch. I just - do we - I mean, do you just - there's pronghorn everything out here. What's your reaction to that? I mean, that's kind of ironic, huh?

VIRGINIA GOULDSBURY: Well, it will be ironic if it all gets developed and there's no pronghorn out here. But half the streets are named pronghorn lane, road. Some of the subdivisions are Pronghorn Ranch. It was used as, you know, back, you know, 20 years ago, it was used as advertisement to have people come out here and move and build houses by a lot of the developers to, you know, say come live with the pronghorn, and a lot of people moved here for it.

MORALES: The antelope are unique. They're the fastest animal in North America. They can maintain speeds up to 60 miles per hour. But they're also very high strung. The idea of crossing a road overwhelms them. When Game and Fish has tried to relocate pronghorn, Mocarski says a few typically suffer what's called capture myopathy.

ZEN MOCARSKI: For a human, it would be similar to a heart attack in that they get - they just over-stress. And their heart begins to beats so fast and it stops.

MORALES: Back in the early '90s, Prescott developers built a subdivision where a large herd of pronghorn lived. Game and Fish tried to relocate some of the animals. A few died in the process. When people found out, they protested. Mocarski says Game and Fish backed off but warned that without relocation, the entire herd would die a slow death.

MOCARSKI: It took less than a decade from - for that herd of 129 to go from 129 down to 100, down to 90, down to 50 to the point today where there are zero. There are none left. And it just proves the point that the do-nothing approach doesn't work.

MORALES: He says the antelope died for several reasons. The animals' primary defenses are their tremendous eyesight and speed. They need wide-open grassland to see a predator coming. When antelope are confined to a small space, inbreeding becomes a problem.

This winter, Game and Fish relocated eight antelope from this area. Volunteers in Southern Arizona removed almost 4,000 acres of mesquite and modified 50 miles of fences so the reintroduced antelope could crawl under them. Across the state, researchers are also working on rebuilding wildlife corridors over roads and through private land so the animals aren't so confined. In Prescott Valley, Mocarski and Gouldsbury drive down a newly paved road when we finally spot a couple pronghorn way off in the distance.

Oh, I see them. Wow.

For HERE AND NOW, I'm Laura Morales in Prescott Valley, Arizona.

YOUNG: And Laura's story comes to us from the Fronteras Desk, a public radio collaboration in the Southwest that focuses on the border, immigration and changing demographics. Transcript provided by NPR, Copyright NPR.